1 - Anatomy & Physiology of Inner Ear Flashcards
What do we call the canals that house the inner ear?
The labyrinth
Where is the part of the ear that is not visible embedded?
The temporal bone
What are the three parts of the inner ear?
Semicircular canals
Vestibule
Cochlea
Impedence
The sum of all energy that opposes the transmission of sound
What happens if the impedance of two mediums is unequal?
It is not possible to easily transmit sound from one to the other
What creates the impedance balance of the inner ear? What does this require?
The inner ear fluids create the impedance imbalance
This means more energy is required to produce a sound wave
What is the function of the cochlea?
To transduce mechanical energy into electrical or neural energy
What two things does the oval window connect?
The stapes to the cochlea
What is the cochlea’s inner wall called?
The modiolus
What is the name of the small bony shelf that protrudes from the modiolus?
Spiral Lamina
Where is perilymph found?
In the scala vestibuli and the scala tympani
What is the name for the small opening at the apical end of the cochlea?
Helicotrema
The oval window transmits vibration into the ___________.
Scala vestibuli
The round window terminates the __________.
Scala tympani
What is the triangular sac of fluid that runs the entire length of the cochlea?
Scala Media
Cochlear Duct
What separates the scala media from the scala tympani?
Basilar membrane
What separates the scala media from the scala vestibuli?
Reissner’s Membrane?
How thick is Reissner’s membrane?
1-2 cells only
What is the purpose of the stria vascularis?
It supplies blood to the organ of corti.
It maintains its metabolic processes and balances
What is the triangular shaped tunnel that gives structure to the organ of corti?
The tunnel of corti
Where can cordilymph be found?
In the tunnel of corti
How many inner hair cells do humans have?
Around 3500
How are inner hair cells arranged?
In small bundles of 40-60 stereocillia.
These are arranged in a U-shape
What are the cup-like cells that support the hair cells?
Dieter’s cells
What are the cells that press laterally on the inner hair cells to help hold them in place?
Cells of Hensen
How many rows of outer hair cells do humans have?
3-5
How many stereocilia are on each outer hair cell?
150
How are the stereocilia of outer hair cells arranged?
In a V or W shape
What happens as a result of the stapes moving the inner ear fluid?
A pressure wave is generated in the fluid along the basilar membrane
This deflects as a traveling wave
What is the maximal deflection of the basilar membrane dependent on?
The frequency of the input
High frequency sounds produce maximal displacement at the the basal end of the cochlea
Low frequency sounds produce maximal displacement at the the apical end of the cochlea
What happens when the stereocilia are sheared?
5
The tip links are tightened (IHC)
This causes the ion channels to open
The causes an influx of potassium ions (K+)
This releases neural transmitters that stimulate the spiral ganglion
This generates an action potential
What is depolarization?
Making a cell more positive or negative
Endocochlear Potential
The resting potential of endolymph
Approximately 80 mV
What is the intercellular resting potential?
-70mV
What is the difference between the resting potential of endolymph and that of hair cells?
80 mV + (-70) mV
= 150 mV
This is the highest voltage difference in the entire body
What is responsible of maintaining resting potentials?
Stria Vascularis
What happens when there is damage to the stria vascularis?
The resting potential difference is reduced and the ear becomes less sensitive
Cochlear Microphonic
Only observable when a stimulus is present
Mimics the acoustical input’s frequency and input
What is the magnitude of the cochlear microphonic proportional to?
The displacement of the basilar membrane
Action Potential
Sum of many individual neurons firing simultaneously
It starts out negative, gradually becomes positive, then becomes negative again.
It reflects the electrical activity of the cochlea
Summating Potential
A DC potential that only occurs with acoustic stimulation
Can be positive or negative
What happens because the outer hair cells touch the tectorial membrane?
The inner hair cells are more likely to be stimulated by fluid motion
Motility
The Outer Hair Cells ability to change size
How fast does the motility of the outer hair cells change?
Very rapidly (tenths of milliseconds)
Very slowly (several seconds)
What does the motility of the outer hair cells accomplish?
It changes the overall mechanical stiffness of the basilar and tectorial membrane
What causes cochlear emissions?
The motility of the outer hair cells
Otoacoustic Emissions
Provide amplification
Narrowband acoustic signals generated by ears that hear normally
Can occur with or without stimulation
Spontaneous Emissions
Otoacoustic Emissions that occur without a stimulus
Evoked Emissions
Otoacoustic Emissions that occur with a stimulus
What causes most forms of hearing impairment?
The weakening or loss of otoacoustic emissions (OAEs)
What do we call the cavity in the temporal bone which houses the inner ear?
Labyrinth
What types of labyrinths are there?
Bony Labyrinth
Membranous Labyrinth
Where do we get the word labyrinth?
From Greek
It means a maze
How many turns does the cochlea have?
2 1/2
What is the “window” part of the oval window and the round window?
Skin
What is the purpose of the round window?
It equalizes the pressure created when the stapes presses the oval window
What fills the bony labyrinth?
Perilymph
What is perilymph similar to?
Cerebrospinal Fluid
What does perilymph have a similar ionic composition to?
Extracellular Fluid
Where can you find perilymph?
Scala Vestibuli
Scala Tympani
Vestibule
What is the membranous labyrinth composed of?
4
Semicircular canals
Utricle
Saccule
Scala Media
What does Reissner’s Membrane do?
Separates the Scala Vestibuli from the Scala Media
What does the Spiral Ligament do?
Holds the membranes in place
What is the function of the Basilar Membrane?
Separates the Scala Tympani from the Scala Media
Houses the sensory cells
What is the Osseous Spiral Lamina?
A thin shelf of bone
Where is the Basilar Membrane the widest?
At the Apex
Where is the Basilar Membrane the stiffest?
At the base
Where is the basilar membrane the narrowest?
The base
Where does the basilar membrane have more mass?
The apex
Where is the basilar membrane less stiff?
The apex
Where is the basilar membrane the most tense?
The base
Where is the basilar membrane the most flaccid?
The apex
How can otoacoustic emissions be measured (OAEs)?
By inserting a tiny microphone at the entrance of the ear canal
What is a kinocilium?
It is the tallest of the stereocilia
What happens when the outer hair cells are pushed by the basilar membrane into the tectorial membrane?
The stereocilia are pushed into the kinocilium
What happens when the basilar membrane pulls away from the tectorial membrane?
The stereocilia are bent away from the kinocilium
What are the pivot points in the organ of corti?
The points where the basilar membrane connects to the spiral lamina and the spiral ligament.
This is where the membrane starts to move
Which part of the basilar membrane moves the slowest?
The apex
Which part of the basilar membrane moves the fastest?
The base
Which hair cells are damaged or die first?
The high frequencies at the base of the cochlea
This is probably due to the scrubbing or shearing motion
…or the continual pounding of the stapes at the oval window for noise induced loss
What makes the inner hair cells move back and forth?
The movement of the fluid between the basilar and tectorial membranes
What is the resting potential of perilymph?
0-5 mV
What is the resting potential of Endolymph?
80 mV
What kind of electrical charge do hair cells have?
Highly negative
Can a malfunctioning stria vascularis cause hearing loss?
Yes.
What is a good metaphor for the stria vascularis?
The battery of the cell
What does the stria vascularis do?
It pumps charged (+) ions into the hair cells and then pumps them out again
For the outer hair cells, current causes ___________.
The hair cell to exhibit “motility” or movement
How do the outer hair cells move?
They lengthen and shorten
What allows the outer hair cells to move?
The reaction of prestin to potassium
For the outer hair cells, motility _________.
Generates force
How does the outer hair cells’ motility affect the basilar membrane?
It increases its displacement
For the outer hair cells, the increase of input from the OHC’s motility is called ____________.
Cochlear Amplification
The cochlear amplifier effect _______ and ________ for _______.
Improves the sensitivity
Improves frequency selectivity
The Basilar Membrane
When does the basilar membrane exhibit a passive response?
When there is hearing loss
When does the basilar membrane exhibit an active response?
When there is normal hearing
Where is fluid pumped from during the up and down motion of the basilar membrane?
Internal Spiral Sulcus
What are the different ways the sound signal is transduced?
4
Mechanically
Hydromechanically
Electrochemically
Electrically
How is the sound signal transduced mechanically?
4
Tympanic Membrane
Ossicular & Stapes Movement
Traveling Wave
Shearing of the Stereocilia
How is the sound signal transduced hydromechanically?
Movement of the perilymph within the cochlea
How is the sound signal transduced electrochemically?
The change in the ionic composition within the hair cell
How is the sound signal transduced electrically?
Action potential
What causes shearing of the stereocilia?
The movement of the basilar membrane
